I bumped this because I have a 55 shrimp tank with same problem. I can't use much of anything to attempt to kill it and its all over gravel. I have a high tech setup and C02 is what will take care of it but I'm already in a light green color on drop checker. I backed my lights off from 12 to 8 hours. I think this all started when I started filling with aged water. I noticed this BBA starting about a month after. I'm treating my 75 ( which is right next to it with algae fix and double dose of excel and everything has recovered nicely but doesn't seem to be affecting the BBA on gravel here either. I probably have 100 + cherrys in there and would be nearly impossible. The aged water has a heater and bubbles in it and there is something about that water I think started this issue. Th Amis in advance